U.S. patent number 5,109,106 [Application Number 07/482,509] was granted by the patent office on 1992-04-28 for preparation of amorphous/semicrystalline semi-aromatic (co)polyamides from alkyl pentamethylene diamine.
This patent grant is currently assigned to Rhone-Poulenc Chimie. Invention is credited to Pierre-Yves Lahary, Serge Roy.
United States Patent |
5,109,106 |
Lahary , et al. |
April 28, 1992 |
Preparation of amorphous/semicrystalline semi-aromatic
(co)polyamides from alkyl pentamethylene diamine
Abstract
Amorphous or semicrystalline semi-aromatic copolyamides are
prepared, with significantly reduced loss of amino reactant, by
polycondensing an acidic monomer which includes at least one
aromatic dicarboxylic acid having from 8 to 18 carbon atoms with an
amino comonomer consisting essentially of an
alkylpentamethylenediamine, or salt thereof, wherein said
polycondensation is carried out in a closed reaction zone.
Inventors: |
Lahary; Pierre-Yves (Lyons,
FR), Roy; Serge (Charly, FR) |
Assignee: |
Rhone-Poulenc Chimie
(Courbevoie, FR)
|
Family
ID: |
9379120 |
Appl.
No.: |
07/482,509 |
Filed: |
February 21, 1990 |
Foreign Application Priority Data
|
|
|
|
|
Feb 21, 1989 [FR] |
|
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89 02467 |
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Current U.S.
Class: |
528/349; 528/338;
528/340; 528/336; 528/339; 528/347 |
Current CPC
Class: |
C08G
69/26 (20130101); C08G 69/28 (20130101) |
Current International
Class: |
C08G
69/26 (20060101); C08G 69/28 (20060101); C08G
69/00 (20060101); C08G 069/28 () |
Field of
Search: |
;528/349,347,338,339,340 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Chemical Abstracts, vol. 71, No. 24, Dec. 15, 1969, p. 75, No.
114079d, Columbus, Ohio, U.S.; & JP-A-69 19551 (Toyo Rayon Co.,
Ltd.) Aug. 23, 1969..
|
Primary Examiner: Anderson; Harold D.
Attorney, Agent or Firm: Burns, Doane, Swecker &
Mathis
Claims
What is claimed is:
1. A process for the preparation of an amorphous or semicrystalline
semi-aromatic (co)polyamide, comprising polycondensing a starting
monomer/comonomer composition comprising an acidic monomer which
comprises at least one aromatic dicarboxylic acid having from 8 to
18 carbon atoms with an amino comonomer consisting essentially of
an alkylpentamethylenediamine, or salt thereof, in a closed
reaction zone and which further comprises:
(a) stage 1: progressively increasing the temperature of the
starting monomer/comonomer composition to a certain value T1 above
110.degree. C.; then, at a constant pressure P equal to the
autogenous steam pressure attained, which is higher than
atmospheric pressure, removing the water present in the reaction
mass by steady distillation while simultaneously progressively
increasing the temperature of the reaction mass to a value T2 which
is higher than the temperature T1 attained prior to
distillation;
(b) stage 2: progressively decreasing the pressure from such
autogenous pressure to atmospheric pressure with or without
simultaneously increasing the temperature of the reaction mass to a
value T3 which is higher by some ten to several tens of degrees
centigrade than the temperature T2 attained prior to decompression,
while continuously maintaining said steady distillation of water
during said period of decompression;
(c) stage 3: completing the polycondensation by stirring the
reaction mass at atmospheric pressure or at a lower pressure with a
mass temperature equal to or higher than the temperature T2 or T3
attained at the end of stage 2, for a sufficient period of time as
to produce a polyamide having the desired molecular and viscosity
characteristics; with the provisos that:
(d) the starting monomer/comonomer composition includes sufficient
amount of water as to permit the distillation of stage 1 to be
carried out under the particular conditions of temperatures (T1 and
T2) and pressure (P) indicated below, and
(e) the temperature of the starting composition in said closed
reaction zone is progressively increased in the stage 1 to a value
T1 ranging from 160.degree. C. to 190.degree. C.; then, at a
constant pressure P equal to the autogenous steam pressure
attained, ranging from 0.5 to 1.2 MPa, removing the water present
in the reaction mass by steady distillation by simultaneously
progressively increasing the temperature of the reaction mass to a
value T2 ranging from 210.degree. C. to 235.degree. C.
2. The process according to claim 1, wherein the starting
composition in stage 1 is in the form of an aqueous dispersion or
an aqueous solution of a salt, wherein the quantity of water
corresponds to that permitting the distillation in stage 1 to be
conducted at the conditions of temperature (T1 and T2) and of
pressure (P) recited in claim 1.
3. The process according to claim 1, wherein an amount of amino
comonomer is introduced in addition to the acidic monomer in stage
1, said amount of amino comonomer being greater than the
stoichiometric amount of COOH and NH.sub.2 groups in the starting
composition.
4. The process according to claim 3, wherein the excess amount of
amino comonomer, expressed as the molar percentage of excess amino
comonomer, according to the relationship: ##EQU3## is in the range
of from about 0.5 to 7%.
5. The process according to claim 1, wherein said acidic monomer is
terephthalic acid, isophthalic acid or a mixture thereof and said
amino comonomer is 2-methyl-1,5-pentamethylenediamine or a
combination of 2-methyl-1,5-pentamethylenediamine and not more than
15 mol % of 2-ethyl-1,4-tetramethylenediamine.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the preparation of amorphous or
semicrystalline semi-aromatic (co)polyamides from an acidic monomer
comprising at least one aromatic dicarboxylic acid having from 8 to
18 carbon atoms and from an amino comonomer predominantly
comprising an alkylpentamethylenediamine.
2. Description of the Prior Art
Polyamides prepared from aliphatic diamines and from aromatic
dicarboxylic acids have long been known to this art. Depending on
their composition, these polyamides are: either semicrystalline
polymers which have a high glass transition temperature T.sub.g,
generally above 120.degree. C., and a melting temperature T.sub.m
well above 300.degree. C., which is not compatible with facile
melt-processing; or amorphous polymers which combine a T.sub.g
which frequently exhibits medium values of 100.degree. C. to
120.degree. C. with a processing temperature which is not
excessively high, on the order of 200.degree. to 290.degree. C. The
semicrystalline polyamides are advantageously employed when it is
intended, for example, to manufacture shaped articles which exhibit
an excellent dimensional stability and an excellent retention of
mechanical properties at high temperatures, as a result of the high
value of the T.sub.g of the polymer employed. The amorphous
polyamides are advantageously employed in fields which require, for
example, an excellent transparency in the case of the fabricated
shaped articles.
Semicrystalline polyamides of particular interest are those
prepared from 2-methyl-1,5-pentamethylenediamine and terephthalic
acid (cf. JP-A-69/019,551) because of the possibility of providing
a T.sub.g on the order of 142.degree. C., while having a T.sub.m
which remains below 290.degree. C. This permits the polymer to be
processed according to the usual techniques employed for the
conversion of polyamide 66. Amorphous polyamides of particular
interest are those also prepared from
2-methylpentamethylenediamine, but reacted with a mixture of
terephthalic acid and of isophthalic acid (15 to 30 mol % in the
mixture of the diacids) (cf. FR-A-2,325,673). These latter polymers
offer the possibility of providing a T.sub.g value which is high
for an amorphous polymer and which, here again, can be as high as
142.degree. C.
A convenient operating procedure for preparing these semi-aromatic
polyamides of particular interest entails the conventional
polycondensation process used to prepare nylon 66, carried out in
liquid phase or in the melt. According to this process, the
polycondensation is carried out starting with compositions which
either contain stoichiometric or essentially stoichiometric amounts
of diamine and of diacid, or contain their salt, the operation
being carried out in a closed system of the autoclave type,
optionally in the presence of water and wherein the following
stages are conducted in sequence:
(a) Stage 1: in which, with the autoclave closed, the temperature
of the starting composition is progressively increased up to a
value ranging from 200.degree. C. to 240.degree. C.; then, at a
constant pressure equal to the autogenous steam pressure obtained,
which, for example, ranges from 1.5 to 2.5 MPa when the starting
composition contains water, removing the water present in the
reaction mass by steady distillation by simultaneously
progressively increasing the temperature of the mass to a value in
the range of from 245. to 280.C;
(b) Stage 2: in which the pressure is progressively decreased from
the value of the autogenous pressure to the value of the
atmospheric pressure and, simultaneously, the temperature of the
reaction mass is optionally increased to a value which is some ten
to several tens of degrees centigrade higher than the temperature
attained before decompression, while ensuring a steady distillation
of water during this decompression period; and
(c) Stage 3: in which the polycondensation is completed by stirring
the reaction mass for a certain period of time, the operation being
carried out at atmospheric pressure and optionally (or) at a lower
pressure with a mass temperature equal to or higher than the
temperature attained at the end of Stage 2, until the point in time
when the polyamide has attained the desired molecular and viscosity
characteristics.
However, carrying out such a conventional polycondensation process
is not free from disadvantages when the starting amino comonomer is
an alkylpentamethylenediamine such as
2-methyl-1,5-pentamethylenediamine because of the development of
interfering reactions involving this diamine.
2-Methyl-1,5-pentamethylenediamine is a compound which cyclizes
readily; when involving the free diamine, this cyclization produces
3-methyl piperidine (a product designated hereinafter by the
expression: "free cyclic amine") with a release of ammonia NH.sub.3
and, when it entails the diamine participating in the amidification
reactions via only one of its functional groups, it serves as a
chain-limiting mechanism, producing blocking groups of the formula:
##STR1## also with release of ammonia. The free cyclic amine formed
is recovered during Stages 1 and 2 at the time when water is
removed by distillation at constant pressure (Stage 1) and then
during the decompression (Stage 2). Another interfering reaction
includes the loss of the amino reactant
(2-methylpentamethylenediamine) by entrainment, which takes place
essentially completely during Stages 1 and 2 at the time of the
removal of the water present by distillation at constant pressure
(Stage 1) and then during the decompression (Stage 2). The result
of these interfering reactions, therefore, presents two
disadvantages:
(i) on the one hand, a high loss of total basicity, which is equal
to at least 4.5%, involving, first, a departure from stoichiometry
during the polycondensation between the primary amino groups and
the carboxyl groups which react, consequently preventing the
likelihood of readily increasing the molecular weight of the
polyamide being formed and, secondly, an actual difficulty in
reproducing the process on an industrial scale. The loss in total
basicity described above is established in relation to the total
amount of amino reactant introduced and is expressed by the
equation: ##EQU1## the expression "basicity lost" corresponds to
the sum: number of NH.sub.2 equivalents of amino reactant which is
lost during distillation+number of NH equivalents of free cyclic
amine+number of NH.sub.2 equivalents of ammonia. This lost basicity
is measured directly, using potentiometric determination, on the
distillates, i.e., on all of the water condensed during the
distillation stages at constant autogenous pressure and during the
decompression. It is possible to measure the number of NH
equivalents of free cyclic amine alone, again using a
potentiometric determination, by performing the operation on the
distillates, but after they have been treated such as to
differentiate between the free cyclic amine and other basicities
(amino reactant and ammonia);
the expression "basicity introduced" corresponds to the number of
NH.sub.2 equivalents of the amino comonomer introduced. The
expression "number of" primary or secondary amino "equivalents" of
a compound connotes the number of primary or secondary amino groups
present in one mole of said compound; for example, 1 mole of amino
reactant consisting of 2-methylpentamethylenediamine contains 2
primary amino NH.sub.2 equivalents, whereas one mole of cyclic
amine consisting of 3-methylpiperidine contains one secondary amino
NH equivalent; and
(ii) on the other hand, the existence in the polycondensation
mixture of a high proportion of end groups of the cyclic amine
type, which serve as a chain-limiter and can restrict the access to
high molecular masses. It should be noted that this second
disadvantage is less awkward than the first, relating to the loss
in total basicity.
Overall, the above disadvantages associated with the use of an
amino reactant such as an alkylpentamethylenediamine, capable of
being readily entrained by distillation and cyclized by a reaction
that produces products which are useless in the polycondensation,
make it impossible to carry out the conventional process used to
prepare nylon 66.
SUMMARY OF THE INVENTION
Accordingly, a major object of the present invention is the
provision of an improved process for the preparation of amorphous
or semicrystalline semi-aromatic polyamides from an amino reactant
predominantly comprising an alkylpentamethylenediamine, in
particular 2-methyl-1,5-pentamethylenediamine, which improved
process is of modified nylon 66 type and which reduces the
competing reactions to date characterizing the state of this art
such that, in particular, any loss in total basicity is decreased
to values of less than 4%.
Briefly, the present invention features a process for the
preparation of amorphous or semicrystalline semiaromatic
(co)polyamides, comprising polycondensing either an acidic reactant
containing at least one aromatic dicarboxylic acid having 8 to 18
carbon atoms and an amino reactant essentially consisting of an
alkylpentamethylenediamine, or salt thereof, with the
polymerization being carried out in a closed system of the
autoclave type in the following sequence of stages:
(a) Stage 1: in which, the autoclave being closed, the temperature
of the starting composition is progressively increased to a certain
value T1 above 110.degree. C.; then, at a constant pressure P equal
to the autogenous steam pressure attained which is higher than
atmospheric pressure, the water present in the reaction mass is
removed by steady distillation while the temperature of the
reaction mass is simultaneously progressively increased to a value
T2 which is higher than the temperature T1 attained before
distillation;
(b) Stage 2: in which the pressure is progressively decreased from
the value of the autogenous pressure to the value of the
atmospheric pressure and the temperature of the mass is
simultaneously optionally increased to a value T3 which is higher
by some ten to several tens of degrees centigrade than the
temperature T2 attained before decompression, while continuously
ensuring a steady distillation of water during this decompression
period; and
(c) Stage 3: in which the polycondensation is completed by stirring
the reaction mass for a certain period of time, the operation being
carried out at atmospheric pressure and optionally (or) at a lower
pressure with a mass temperature equal to or higher than the
temperature T2 or T3 attained at the end of Stage 2, for a
sufficient period of time to produce a polyamide having the desired
molecular and viscosity characteristics; and wherein such
polycondensation:
(d) the starting material composition, on the one hand,
additionally necessarily contains water in sufficient amount to
permit the distillation of Stage 1 to be conducted under the
particular conditions of temperatures (T1 and T2) and of pressure
(P) which are indicated below and, on the other hand, additionally,
but optionally, contains a catalyst; and
(e) in Stage 1, after the autoclave has been closed, the
temperature of the starting composition is progressively increased
to a value T1 ranging from 160.degree. C. to 190.degree. C.; then,
at a constant pressure P equal to the autogenous steam pressure
attained, which ranges from 0.5 to 1.2 MPa, the water present in
the reaction mass is removed by steady distillation by
simultaneously progressively increasing the temperature of the
reaction mass to a value T2 ranging from 210.degree. C. to
235.degree. C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
More particularly according to the present invention, the subject
process can be carried out using either stoichiometric amounts of
an acidic reactant and of an amino reactant contributing equivalent
numbers of COOH and NH.sub.2 groups, or the stoichiometric salt(s)
thereof.
It may prove advantageous to introduce amounts of amino reactant
which are greater than those precisely required to establish the
equivalence between the COOH and NH.sub.2 groups in the starting
compositions, such as to introduce into the reaction mass an excess
of diamine(s) which makes it possible to compensate for the loss of
this reactant which occurs during the operation of distillation at
constant autogenous pressure (Stage 1), and then during the
decompression operation (Stage 2). According to this preferred
embodiment, the excess of amino reactant, expressed as the molar
percentage of excess amino reactant according to the relationship:
##EQU2## typically ranges from 0.5 to 7% and, preferably, from 1 to
5%.
Starting compositions prepared from:
(i) acidic reactant: terephthalic acid and/or isophthalic acid;
(ii) amino reactant: 2-methyl-1,4-pentamethylenediamine, either
alone or mixed with not more than 15 mol % of
2-ethyl-1,4-tetramethylenediamine, are well suited for carrying out
the process according to the present invention. To prepare
amorphous semi-aromatic polyamides, an acidic reactant comprising a
mixture of terephthalic acid with at least 10 mol % (in the mixture
of the two acids) of isophthalic acid is advantageously employed.
To prepare semicrystalline semi-aromatic polyamides, a reactant
solely comprising terephthalic acid is advantageously employed. The
synthesis of the 2-methylpentamethylenediamine starting material
can be performed by hydrogenation of the dinitrile of 2-methyl
glutaric acid according to processes well known to this art.
Similarly, the synthesis of 2-ethyltetramethylenediamine can be
performed by hydrogenation of the dinitrile of 2-ethylsuccinic
acid.
The process according to the present invention will now be
described in greater detail.
The expression "water present in the reaction mass" (which appears
above in Stage 1 concerning the distillation) is intended to define
the water contained in the starting compositions plus the water
which may be formed by the polycondensation of the acidic monomer
and the amino comonomer. The amount of water contained in the
starting compositions is not critical, provided it makes it
possible to conduct the distillation of Stage 1 under the
particular conditions of temperatures (T1 and T2) and of autogenous
pressure (P) indicated above; this amount of water can easily be
determined by one skilled in this art.
To carry out Stage 1 of the process according to the invention, it
is possible to introduce into the reactor starting compositions
which are in the form of mixtures: either based on the acidic
reactant, the amino reactant, water and optionally on the catalyst,
the acidic reactant being employed in the solid state and the amino
reactant being employed, for example, in the state in which it is
found naturally, or in the form of an aqueous solution; or based on
the salt(s) of diacid(s) and of diamine(s), water and optionally on
the catalyst, the salt(s) being employed, for example, in the solid
state, in aqueous dispersion, or in the form of an aqueous solution
thereof.
In a preferred embodiment of Stage 1, starting compositions are
employed which are in the form of an aqueous dispersion or of an
aqueous solution of salt(s) derived from diacid(s) and from
diamine(s), optionally additionally containing a catalyst, in which
the amount of water employed is advantageously equal to that which
corresponds to the water contained in the starting compositions. To
provide the stoichiometry and optionally the desired excess of the
stoichiometry by adding diamine(s) in the production of the
salt(s), the operation is carried out by precise weighing of the
reactants whose strength is perfectly known at the time of use; it
is preferable to subsequently monitor this stoichiometry by
measuring the pH of sample solutions obtained by diluting the
salt(s) in a suitable solvent such as, for example, water.
When the process according to the present invention is carried out
using the suitable starting compositions described above, namely,
those prepared from an acidic reactant based on terephthalic acid
and/or isophthalic acid and from an amino reactant based on
2-methylpentamethylenediamine and optionally
2-ethyltetramethylenediamine, the aqueous dispersion or the aqueous
solution of salt(s) which is used has a water content whose lower
limit ranges from 25 to 31% by weight, relative to the total amount
of salt(s)+water, depending on the nature of the acidic reactant
(maximum concentration of salt(s) ranging from 69 to 75% by
weight). With regard to the upper limit of the water content, this
is generally equal to 50% by weight (minimum 50% salt(s)
concentration). It is apparent, in the case where the aqueous
dispersion or the aqueous solution of salt(s) has a water content
which must be lowered, especially when it is higher than 50% by
weight, that a concentration of the starting composition can be
conducted in a first step, before beginning Stage 1, for example by
evaporating the water off at atmospheric pressure or at a pressure
slightly above atmospheric pressure and under low temperature
conditions which absolutely do not permit the development of
amidification reactions and/or of the interfering competing
reactions discussed above.
With regard to the catalyst which may be employed, this generally
is either a compound (.alpha.) or a compound (.beta.), (.alpha.)
denoting an inorganic oxygenated mono- or polyacid or an organic
oxygenated mono- or polyacid other than a carboxylic acid, in which
at least one of the acidic functional groups has an ionization
constant pK.sub.a equal to or less than 4 in water at 25.degree.
C., (.beta.) denoting an alkali or alkaline earth metal salt of
this acid.
Exemplary of the strong acids which are suitable, the following are
representative:
(i) among the inorganic oxyacids, sulfurous, sulfuric,
hypophosphorous, phosphorous, orthophosphoric or pyrophosphoric
acids;
(ii) among organic oxyacids:
organosulfonic acids of the formula R.sub.1 --SO.sub.3 H (I) in
which R.sub.1 is a linear or branched chain alkyl radical having
from 1 to 6 carbon atoms, a phenyl radical optionally substituted
by 1 to 3 alkyl radicals having from 1 to 3 carbon atoms, a
phenylalkyl radical having from 1 to 3 carbon atoms in the alkyl
moiety and whose benzene nucleus may be optionally substituted by 1
to 3 alkyl radicals having from 1 to 3 carbon atoms, or a naphthyl
radical optionally substituted by 1 to 4 alkyl radicals having from
1 to 3 carbon atoms;
organophosphonic acids of the formula R.sub.2 --P(O)(OH).sub.2 (II)
in which R.sub.2 is an alkyl radical, a phenyl radical or a
phenylalkyl radical, with such radicals being as defined above for
R.sub.1 ;
organophosphonic acids of the formula R.sub.3 R.sub.4 --P(O)(OH)
(III) in which each of R.sub.3 and R.sub.4, which may be identical
or different, is a linear alkyl radical having from 1 to 3 carbon
atoms, a phenyl radical or a phenylalkyl radical, with each of
these latter two radicals being as defined above for R.sub.1 ;
organophosphonous acids of the formula R.sub.5 --H--P(O)(OH) (IV)
in which R.sub.5 is a linear or branched chain alkyl radical having
from 1 to 4 carbon atoms (branching being excluded in the case of
an alkyl radical having 4 carbon atoms), a phenyl radical or a
phenylalkyl radical, each of these latter two radicals being as
defined above for R.sub.1.
As the strong acid (.alpha.), it is preferred to use the acids
derived from phosphorus and more particularly hypophosphorous,
phosphorous, orthophosphoric, pyrophosphoric, methylphosphonic,
phenylphosphonic, benzylphosphonic, dimethylphosphinic,
diphenylphosphinic, methylphenylphosphinic, dibenzylphosphinic,
methylphosphonous, phenylphosphonous or benzylphosphonous
acids.
With regard to the acid salt (.beta.), an alkali metal or alkaline
earth metal salt derived from the inorganic or organic oxyacids
(.alpha.) is advantageously used.
As the salt (.beta.), it is preferred to use those which are
completely soluble in the reaction mixture. Among these preferred
salts (.beta.), those which are especially suitable are the sodium
and potassium salts derived from the particular types of inorganic
or organic oxyacids (.alpha.) which are useful, referred to above.
Salts (.beta.) which are very particularly useful are the sodium
and potassium salts derived from the preferred phosphorous-derived
acids named above.
The proportions of strong acid (.alpha.) or of salt (.beta.),
expressed as a percentage by weight relative to the final
polyamide, generally range from 0.01 to 1% and preferably from 0.01
to 0.5%.
With respect to the operation of Stage 1 of the process according
to the present invention, it should be appreciated that the
progressive heating of the starting composition up to the
temperature T1 can be carried out over a period of time ranging,
for example, from 10 minutes to 2 hours. As for the distillation
under constant autogenous pressure P, this is carried out over a
period of time ranging, for example, from 30 minutes to 3 hours, 30
minutes.
In the operation of Stage 1, it will be preferred to conduct the
distillation at a constant autogenous pressure P ranging from 0.6
to 1 MPa by selecting: a temperature T1 at the start of
distillation ranging from 170.degree. C. to 185.degree. C. and a
temperature T2 immediately prior to decompression ranging from
215.degree. C. to 230.degree. C.
In the operation of Stage 2, the decompression, which may progress
in successive plateaus, is carried out over a period of time
ranging, for example, from 20 minutes to 2 hours, 30 minutes and
the temperature of the reaction mass is simultaneously increased to
a value T3 ranging, for example, from 250.degree. C. to 320.degree.
C.
In the operation of Stage 3, the polycondensation is finished by
permitting the reaction mass to react at the temperature T3 or at a
temperature which may be higher than T3 by a few degrees to about
ten degrees, preferably while operating at a reduced pressure in
the range of from 1.times.10.sup.2 to 1,000.times.10.sup.2 Pa for a
period of time (including the time for reducing pressure) ranging,
for example, from 10 minutes to 3 hours.
Strict observance of the operating conditions described above and,
in particular, observance of the conditions of temperatures
(especially those concerning T1) and of pressure (P) which govern
the distillation at constant pressure in Stage 1, is essential in
order to maintain the loss in total basicity at values of less than
4%. It has unexpectedly been found that the loss in basicity
increases significantly, to exceed the threshold of 4%, both when
the temperature and pressure conditions are above the maximum
limits of the ranges indicated, i.e., 190.degree. C. in the case of
T1 and 1.2 MPa in the case of P, and when these conditions are
below the minimum limits of the ranges indicated, i.e., 160.degree.
C. in the case of T1 and 0.5 MPa in the case of P.
It is apparent that the composition of the starting reactants in
the process according to the invention may also include various
additives which are commonly employed in the preparation of
conventional polyamides. These additives may be, in particular,
nucleating agents and stabilizers of various kinds.
The process according to the invention permits production of
semi-aromatic (co)polyamides which have a viscosity number
(measured in meta-cresol at 25.degree. C. on a solution containing
0.5 g of dried polymer in 100 cm.sup.3 of solvent) which may be
equal to at least 90 ml/g, and this is particularly the case when
the polycondensation is carried out according to the preferred
embodiment of employing an excess of starting amino reactant;
because of the high value of the viscosity characteristics which is
obtained, such (co)polyamides can be converted, for example after
molding, into shaped articles having good mechanical properties.
Furthermore, the (co)polyamides prepared by the process of the
invention are distinguished in that, on the one hand, their
proportions of end COOH and NH.sub.2 groups are essentially
correctly balanced (the difference NH.sub.2 EG - COOH EG, where
NH.sub.2 EG denotes the proportion of NH.sub.2 end groups and COOH
EG denotes the proportion of COOH end groups, being in the range
of, for example, from 0 to 80 meq/kg when taken as an absolute
value; the determination of the proportions of end groups is
carried out as described below) and, on the other hand, their
proportion of chain-limiting end groups of the cyclic amine type is
low and generally below 40 milligram-equivalents per kilogram of
polymer.
The process according to the invention is particularly suited for
discontinuous operation. However, it is also within the ambit of
the present invention to carry it out in a continuous operation by
linking Stage 1 as defined above with a decompression stage and a
finishing stage, overall corresponding to Stages 2 and 3 of the
process of the invention, but with certain adaptations which are
per se known to this art.
In order to further illustrate the present invention and the
advantages thereof, the following specific examples are given, it
being understood that same are intended only as illustrative and in
nowise limitative.
In said examples to follow, a number of controls were carried out.
The particular techniques for implementing such controls are
described immediately below:
I. DETERMINATION OF THE PROPORTIONS OF COOH AND NH.sub.2 END GROUPS
(COOH EG AND NH.sub.2 EG) IN THE POLYMER
This determination was carried out by potentiometric determination
of a solution of polymer in a 70/30 by weight mixture of
trifluoroethanol and chloroform using 0.02N
trifluoromethanesulfonic acid. The method permitted determination
of the COOH and NH.sub.2 groups simultaneously by adding a 0.05N
solution of tetrabutylammonium hydroxide in nitrobenzene. The
results are expressed in milligram-equivalents per kilogram of
polymer (meq/kg).
II. DETERMINATION OF METHYLPIPERIDINE IN THE POLYMER
The determination of 3-methylpiperidine (MPP) in the polymer was
carried out by gas phase chromatography. The principle of the
method was as follows:
(i) the polymer (approximately 250 mg) was first subjected to a
hydrochloric hydrolysis (15 hours at 170.degree. C.) and it was
then neutralized with sodium hydroxide until its pH was slightly
basic;
(ii) the amines were then extracted quantitatively with chloroform
(approximately 50 cm.sup.3); and
(iii) this chloroform extract was finally analyzed by gas phase
chromatography and 3-methylpiperidine was determined by the
internal standard method (internal standard =nonane). The number of
MPP end groups (MPP EG) in the polymer was in this case also
expressed in meq/kg.
III. MEASUREMENT OF THE VISCOSITY NUMBER (IV) OF THE POLYMER
This number was determined at 25.degree. C. according to
International Standard ISO 307, 1977 edition, using a solution
containing 0.5 g of polymer (dried for 2 hours at 60.degree. C.
under an argon purge) in 100 cm.sup.3 of meta-cresol.
IV. DETERMINATION OF THE BASICITY LOST IN THE DISTILLATES
The measurement of this basicity was carried out by a simple
potentiometric determination using HCl in all the water condensed
during the distillation stages at constant autogenous pressure
(Stage 1) and during the decompression (Stage 2).
V. DETERMINATION OF METHYLPIPERIDINE IN THE DISTILLATES
The proportion of 3-methylpiperidine was obtained by a
potentiometric determination of the distillates after specific
reaction with salicylaldehyde, which made it possible to
differentiate between methylpiperidine and other basicities
(2-methylpentamethylenediamine and ammonia).
EXAMPLE 1
This example describes the preparation of an amorphous copolyamide
from isophthalic acid (20 mol % in the mixture of diacids),
terephthalic acid (80 mol % in the mixture of diacids) and
2-methyl-1,5-pentamethylenediamine with a total basicity loss of
3.1%.
(1) Preparation of the methylpentamethylenediamine salt of
(isophthalic+terephthalic) acids in aqueous solution
The operation was carried out in a 10-liter glass reactor
equipped:
(i) with a heating system,
(ii) with an anchor-type stirrer,
(iii) with a system permitting purging of the apparatus with
nitrogen and the maintenance of an oxygen-free atmosphere, and
(iv) with a system enabling the volatile products to be
condensed.
The following materials were introduced cold into the reactor,
which was maintained under a gentle nitrogen purge:
(a) 436.4 g of isophthalic acid (2.6289 moles);
(b) 1,745.5 g of terephthalic acid (10.5151 moles);
(c) 1,524.7 g of 2-methyl-1,5-pentamethylenediamine (13.1440
moles); and
(d) 2,471.1 g of distilled water.
The temperature of the entire mass was increased to 60.degree. C.
and the mixture was stirred for 2 hours while the purging with
nitrogen was continued. The pH of the salt was then adjusted to
7.48.+-.0.05 by successive additions of small quantities of
methylpentamethylenediamine or of a 20/80 mole isophthalic
acid/terephthalic acid mixture (pH measured at 20.degree. C. on an
aqueous solution containing 10% by weight of salt). An aqueous
solution containing 60% by weight of stoichiometric salt was thus
obtained.
61 g (0.5258 moles) of methylpentamethylenediamine were then added;
the pH then attained a value of 9.27; in this example, a molar
excess of 4% of amino reactant was therefore employed.
(2) Polycondensation in an autoclave
The apparatus employed consisted of a 7.5-liter autoclave made of
stainless steel, which was stirred and equipped for operation up to
300.degree. C. and 2.2 MPa in pressure. It was provided:
(i) with a heating jacket system using a heat-transfer fluid;
(ii) with a frame-type stirrer;
(iii) with a system permitting pressurizing with nitrogen;
(iv) with a circuit enabling the volatile products to be condensed
and collected; and
(v) a device for applying a pressure which is lower than
atmospheric pressure.
6 kg of the aqueous salt solution prepared above were introduced
into the autoclave. After 3 nitrogen purges, by pressurizing to
4.times.10.sup.5 Pa followed by decompression, the aqueous salt
solution was concentrated from 60% by weight to 70.6% by weight
over 20 minutes, by evaporating off some of the water present in
the mixture at atmospheric pressure; the temperature then reached
108.5.degree. C.
Subsequently, the following stages were successively carried
out:
Stage 1
The temperature of the aqueous solution containing 70.6% by weight
of salt was increased to T1=174.degree. C. over 50 minutes, while
an autogenous pressure was maintained. A pressure (P) of 0.7 MPa
was then attained. The water present in the reaction mass was then
distilled at a constant pressure of 0.7.+-.0.02 MPa for 1 hour, 40
minutes, such as to provide a mass temperature equal to
T2=224.degree. C.;
Stage 2
Pressure was released to atmospheric pressure over 1 hour and the
temperature of the mass was simultaneously raised to the value
T3=275.degree. C., while a steady distillation of water continued
to be carried out;
Stage 3
A reduced pressure of 750.times.102 Pa was then progressively
established over 30 minutes, while the temperature of the mass was
simultaneously increased to 280.degree. C., and the
polycondensation was finished by continuing to stir the mass at
280.degree. C. at 750.times.10.sup.2 Pa for another 30 minutes.
The stirring was stopped; a nitrogen pressure was then established
in the autoclave and the polymer was drawn off. The latter,
extruded from the autoclave in the form of a strand, was cooled by
passing it through a cold water bath and it was then granulated and
dried.
The polymer obtained was transparent and homogeneous. It exhibited
the following characteristics:
______________________________________ NH.sub.2 EG = 70 meq/kg,
COOH EG = 48 meq/kg, MPP EG = 18 meq/kg, VN = 111 ml/g.
______________________________________
The material balance of basicity was as follows:
(i) basicity introduced: 26.2936 amino equivalents;
(ii) basicity lost in the distillates: 0.8151 amino equivalents
(including 0.2209 amino equivalents in the form of MPP);
(iii) hence, a total basicity loss of 3.1%.
COMPARATIVE EXAMPLE A
In this comparative example, it was shown that, when the
temperature T1 at the start of distillation is higher than
190.degree. C. and the constant autogenous pressure P is higher
than 1.2 MPa (all the other operating conditions being those
described above in Example 1), the polymer which was synthesized
was then obtained with a total basicity loss well above the
threshold of 4%.
The operation was therefore carried out exactly as set forth in
Example 1, with only the following changes being made in respect of
the operation of Stage 1.
The temperature T1 at the start of distillation was equal to
217.2.degree. C., the heating time then being 1 hour, 25 minutes,
and the autogenous pressure P attained was 1.8 MPa. The water
present in the reaction mass was then distilled at a constant
pressure of 1.8.+-.0.02 MPa for 1 hour, 40 minutes, and the
temperature T2 reached at the end of this time was equal to
231.2.degree. C.
The amorphous polymer obtained exhibited the following
characteristics:
______________________________________ NH.sub.2 EG = 26 meq/kg,
COOH EG = 205 meq/kg, MPP EG = 68 meq/kg, VN = 59.5 ml/g.
______________________________________
The material balance of basicity was as follows:
(i) basicity introduced: 26.2936 amino equivalents;
(ii) basicity lost in the distillates: 1.3410 amino equivalents
(including 0.5653 amino equivalents in the form of MPP);
(iii) hence, a total basicity loss of 5.1%.
COMPARATIVE EXAMPLE B
In this comparative example, it was shown that, when the
temperature T1 at the beginning of distillation was below
160.degree. C. and the constant autogenous pressure P was below 0.5
MPa (all the other operating conditions being those described above
in Example 1), the polymer which was synthesized was then also
obtained with a total basicity loss which was higher than the
threshold of 4%.
The operation was therefore carried out exactly according to the
procedure of Example 1, with only the following changes being made
in respect of the operation of Stage 1.
The temperature T1 at the beginning of distillation was equal to
1421.degree. C., the heating time then being 40 minutes, and an
autogenous pressure P of 0.34.+-.0.03 MPa was attained. The water
present in the reaction mass was then distilled at a constant
pressure of 0.34 MPa for 3 hours, 30 minutes, and the temperature
T2 attained at the end of this time period was equal to
224.5.degree. C.
The amorphous polymer obtained exhibited the following
characteristics:
______________________________________ NH.sub.2 EG = 20 meq/kg,
COOH EG = 158 meq/kg, MPP EG = 10 meq/kg, VN = 79.7 ml/g.
______________________________________
The material balance of basicity was as follows:
(i) basicity introduced: 26.2936 amino equivalents;
(ii) basicity lost in the distillates: 1.2016 amino equivalents
(including 0.2209 amino equivalents in the form of MPP);
(iii) hence, a total basicity loss of 4.57%.
EXAMPLE 2
This example describes the preparation of a semicrystalline
polyamide from terephthalic acid and
2-methyl-1,5-pentamethylenediamine with a total basicity loss of
2.6%.
(1) Preparation of the terephthalic
acid/methylpentamethylenediamine salt in aqueous solution:
The operation was carried out as indicated above in Example 1, but
with the following different changes:
(i) 2,295.7 g of terephthalic acid (13.8295 moles);
(ii) 1,604.22 g of 2-methyl-1,5-pentamethylenediamine (13.8295
moles); and
(iii) 2,600 g of distilled water.
Upon completion of salt formation, 64.17 g (0.5532 moles) of
methylpentamethylenediamine were added; the pH then attained a
value of 9.20 and this additional amount of amino reactant
corresponded to a molar excess of 4%. The salt concentration in the
aqueous solution was 60% by weight.
(2) Polycondensation in an autoclave
The operating procedure was the same as that indicated in Example
1, with the following changes:
In respect of Stage 1:
The temperature of the aqueous solution containing 70.6% by weight
of salt was increased to T1=184.degree. C. over 1 hour, while an
autogenous pressure was maintained. A pressure of 0.85 MPa was then
attained. The water present in the reaction mass was then distilled
at a constant pressure of 0.85.+-.0.02 MPa for 1 hour, 40 minutes,
such as to provide a mass temperature equal to T2=225.degree.
C.;
In respect of Stage 2:
The decompression was carried out over two time periods:
(1) decompression down to 0.6 MPa over 1 hour, 30 minutes, while
the temperature of the mass was simultaneously increased to
288.degree. C.; and then
(2) decompression down to atmospheric pressure over minutes, while
the temperature of the mass was simultaneously increased to the
value T3=300.degree. C.;
In respect of Stage 3:
The application of a reduced pressure of 750.times.10.sup.2 Pa and
the final stirring of the mass at reduced pressure were carried out
at an unchanged mass temperature equal to 300.degree. C.
The polymer obtained exhibited the following characteristics:
______________________________________ NH.sub.2 EG = 92 meq/kg,
COOH EG = 55 meq/kg, MPP EG = 31 meq/kg, VN = 114 ml/g.
______________________________________
The material balance of basicity was as follows:
(i) basicity introduced: 26.2934 amino equivalents;
(ii) basicity lost in the distillates: 0.6836 amino equivalents;
and
(iii) hence, a total basicity loss of 2.6%.
While the invention has been described in terms of various
preferred embodiments, the skilled artisan will appreciate that
various modifications, substitutions, omissions, and changes may be
made without departing from the spirit thereof. Accordingly, it is
intended that the scope of the present invention be limited solely
by the scope of the following claims, including equivalents
thereof.
* * * * *